U.S. patent application number 16/767036 was filed with the patent office on 2021-02-04 for porous fiber sheet.
The applicant listed for this patent is Nitto Denko Corporation. Invention is credited to Shigeki ISHIGURO, Hidetoshi MAIKAWA, Tetsuya OTSUKA.
Application Number | 20210035546 16/767036 |
Document ID | / |
Family ID | 1000005177420 |
Filed Date | 2021-02-04 |
United States Patent
Application |
20210035546 |
Kind Code |
A1 |
OTSUKA; Tetsuya ; et
al. |
February 4, 2021 |
POROUS FIBER SHEET
Abstract
This porous fiber sheet is formed using fibers having an average
fiber diameter of 0.5 .mu.m to 20 .mu.m. If the total volume of
solid and gap per unit volume is 100%, the percentage of solid is
1.3% to 8%.
Inventors: |
OTSUKA; Tetsuya; (Osaka,
JP) ; MAIKAWA; Hidetoshi; (Osaka, JP) ;
ISHIGURO; Shigeki; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nitto Denko Corporation |
Osaka |
|
JP |
|
|
Family ID: |
1000005177420 |
Appl. No.: |
16/767036 |
Filed: |
October 23, 2018 |
PCT Filed: |
October 23, 2018 |
PCT NO: |
PCT/JP2018/039361 |
371 Date: |
May 26, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D04H 3/14 20130101; B32B
5/022 20130101; G10K 11/168 20130101 |
International
Class: |
G10K 11/168 20060101
G10K011/168; D04H 3/14 20060101 D04H003/14; B32B 5/02 20060101
B32B005/02 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 2017 |
JP |
2017-227447 |
Claims
1. A porous fiber sheet, comprising: fibers having an average
diameter of 0.5 .mu.m or more and 20 .mu.m or less, wherein a solid
percentage is 1.3% or more and 8% or less when a total volume of a
solid and a gap in a unit volume is taken as 100%.
2. The porous fiber sheet as claimed in claim 1, wherein a total
thickness of the porous fiber sheet is 1 mm or more and 100 mm or
less.
3. The porous fiber sheet as claimed in claim 1, further
comprising: a plurality of nonwoven fabric layers separably and
continuously arranged in a predetermined in-plane direction between
two main surfaces opposite each other, wherein each of the
plurality of nonwoven fabric layers is composed of the fibers being
intertangled as seen from the predetermined in-plane direction.
4. The porous fiber sheet as claimed in claim 3, further
comprising: two skin layers respectively provided on the two main
surfaces opposite each other and composed of a plurality of fibers
that are intertangled as seen from a thickness direction, wherein
the plurality of nonwoven fabric layers is provided between the two
skin layers and formed to be continuous with the two skin layers,
and wherein a thickness of each of the two skin layers is 0.01 mm
or more and 5 mm or less.
5. The porous fiber sheet as claimed in claim 1, wherein the porous
fiber sheet is used as a sound insulating material to attenuate an
incident sound wave.
Description
TECHNICAL FIELD
[0001] The present invention relates to a porous fiber sheet.
BACKGROUND ART
[0002] A porous fiber sheet that attenuates sound waves has been
developed as a noise reduction measure for vehicles, buildings,
household electrical appliances, and the like. (see, for example,
Patent Document 1). The porous fiber sheet of Patent Document 1 has
a C-shaped structure. The porous fiber sheet includes C-shaped and
directly formed fibers and staple fibers having a crimp dispersed
between the directly formed fibers.
PRIOR ART DOCUMENTS
Patent Documents
[0003] Patent Document 1: Japanese Laid-Open Patent Application
Publication No. 2006-506551
SUMMARY OF THE INVENTION
Problem to be Solved by the Invention
[0004] Although sound insulation and a reduction in weight of
porous fiber sheets have been required for a long time, there is a
problem of decreasing the sound insulation properties when the
thickness is reduced due to the reduction in in weight.
[0005] The present invention is made to solve above-described
problems, and the main object of the present invention is to
provide a porous fiber sheet that balances sound insulation and a
weight reduction.
Means for Solving the Problem
[0006] To solve the above-described problem, according to an aspect
of the present invention, there is provided a porous fiber sheet
including: [0007] fibers having an average diameter of 0.5 .mu.m or
more and 20 .mu.m or less, [0008] wherein a solid percentage is
1.3% or more and 8% or less when a total volume of a solid and a
gap in a unit volume is taken as 100%.
Advantageous Effect of the Invention
[0009] According to an aspect of the present invention, a porous
fiber sheet can balance sound insulation and a weight
reduction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a perspective view showing a porous fiber sheet
according to a first embodiment;
[0011] FIG. 2 is a perspective view showing a first modification of
a porous fiber sheet;
[0012] FIG. 3 is a perspective view showing a second modification
of a porous fiber sheet;
[0013] FIG. 4 is a diagram showing a method of manufacturing a
porous fiber sheet according to a first embodiment;
[0014] FIG. 5 is a diagram showing a nonwoven layer formed between
two collectors;
[0015] FIG. 6 is a perspective view showing a porous fiber sheet
according to a second embodiment;
[0016] FIG. 7 is a diagram showing a method of manufacturing a
porous fiber sheet according to a second embodiment;
[0017] FIG. 8 is a diagram showing a porous fiber sheet as a
transversely oriented product obtained in Example 1; and
[0018] FIG. 9 is a diagram showing a porous fiber sheet as a
longitudinally oriented product obtained in Example 5.
EMBODIMENTS FOR CARRYING OUT THE INVENTION
[0019] Hereinafter, embodiments of the present invention will be
described with reference to the drawings. In each drawing, the
description is omitted for the same or corresponding configuration
with the same or corresponding reference numerals.
[0020] FIG. 1 is a perspective view showing a porous fiber sheet
according to a first embodiment. In FIG. 1, the X direction, Y
direction and Z direction are perpendicular to each other. The X
direction is the thickness direction of the porous fiber sheet. The
Y direction and Z direction are an in-plane direction of the porous
fiber sheet. The Z direction is a direction in which a plurality of
nonwoven layers is arranged.
[0021] In FIG. 1, an arrow A represents the incident direction of a
sound wave with respect to the porous fiber sheet 10. Note that the
sound wave is incident perpendicular to the main surface 11 of the
porous fiber sheet 10 in FIG. 1, but may be incident at an oblique
angle. Also, the sound wave may be incident from both sides of the
porous fiber sheet 10 and may be incident on both of the two main
surfaces 11, 12.
[0022] The porous fiber sheet 10 attenuates the incident sound
wave. The porous fiber sheet 10 attenuates the incident sound wave
by converting the energy of the incident sound wave to thermal
energy. When the sound wave enters the porous fiber sheet 10,
because the air vibrates within the porous fiber sheet 10, friction
occurs between the fibers forming the porous fiber sheet 10 and the
air, and the energy of the sound wave is converted to thermal
energy.
[0023] The porous fiber sheet 10 may be used as a sound absorbing
material or as a sound insulating material. The sound absorbing
material is used to inhibit the reflection of a sound wave incident
from a sound source. The sound insulating material is used to
inhibit transmission of a sound wave incident from a sound source.
The porous fiber sheet 10 may also serve as both the sound
absorbing material and the sound insulating material.
[0024] The porous fiber sheet 10 is used to control noises in
vehicles, buildings, household electrical appliances, large
electrical apparatuses, and the like. The vehicles include, for
example, automobiles, trains and airplanes. The vehicle noises
include a running noise, a reflected noise from a tunnel and a
sound barrier wall, and an operating noise from on-board equipment
(for example, air conditioners and engines) in a vehicle. The
buildings include, for example, factories, movie theaters, karaoke
boxes, music halls, and the like. Examples of household electrical
appliances include refrigerators, vacuum cleaners, air conditioner
outdoor units, household storage batteries, and hot water washing
toilet seats. Examples of large electrical apparatuses include
industrial refrigerators.
[0025] The porous fiber sheet 10 may be formed of organic fibers.
The organic fiber materials include general-purpose plastics,
engineering plastics and super engineering plastics. The
general-purpose plastics include polypropylene (PP), polyethylene
(PE), polyurethane (PU), polylactic acid (PLA) and acrylic resins
(for example, PMMA). The engineering plastics include polyethylene
terephthalate (PET), nylon 6 (N6), nylon 6,6 (N66) and nylon 12
(N12). The super engineering plastics include polyphenylene sulfide
(PPS) and liquid crystal polymers (LCP). The porous fiber sheet 10
may be formed of one type of organic fibers or may be formed of
more than one type of organic fibers.
[0026] The porous fiber sheet 10 according to the present
embodiment is formed of organic fibers, but may be formed of
inorganic fibers. Examples of the inorganic fibers include glass
fibers and carbon fibers. The organic fibers and the inorganic
fibers may be combined with each other.
[0027] The average fiber diameter of the porous fiber sheet 10 is
0.5 .mu.m or more and 20 .mu.m or less. If the average fiber
diameter of the porous fiber sheet 10 is 0.5 .mu.m or more, it is
easy to manufacture the porous fiber sheet 10, and the strength of
the porous fiber sheet 10 is sufficient. On the other hand, when
the average fiber diameter of the porous fiber sheet 10 is 20 .mu.m
or less, because the surface area of the fibers per unit volume is
large, friction between the fibers and the air is easily generated
and the sound wave can be effectively attenuated. The average fiber
diameter of the porous fiber sheet 10 is preferably 1 .mu.m or more
and 15 .mu.m or less, and more preferably 1.5 .mu.m or more and 10
.mu.m or less.
[0028] The porous fiber sheet 10 is composed of a solid material,
such as fibers with an average fiber diameter of 0.5 .mu.m or more
and 20 .mu.m or less, and a gap is formed between the fibers. To
improve the sound insulation properties of the porous fiber sheet
10, the inventor of the present invention focused on the solid
occupancy S, which had not been noticed in the conventional related
art.
[0029] The solid occupancy S is the percentage of solids when the
total volume of solids and gaps in the unit volume of the porous
fiber sheet 10 is taken as 100%. That is, the solid occupancy S is
the value obtained by dividing the bulk density (BD) of the porous
fiber sheet 10 by the true density (TD) of the solid (BD/TD) and
multiplying by 100 (BD/TD.times.100). The solid occupancy S is
equal to the value obtained by subtracting the gap percentage from
100.
[0030] The larger the solid occupancy S, the larger the contact
area between air and fibers having an average fiber diameter of 0.5
.mu.m or more and 20 .mu.m or less, and the higher the efficiency
of converting sound wave energy to thermal energy due to the
friction between the fibers and the air, thereby improving the
sound insulation. In contrast, the smaller the solid occupancy S,
the smaller the density and the lighter the weight.
[0031] In the present embodiment, the solid occupancy S is not less
than 1.3% and not more than 8%. When the solid occupancy S is 1.3%
or more, the sound wave is likely to be attenuated by the friction
between the fibers and the air where the average fiber diameter is
0.5 .mu.m or more and 20 .mu.m or less, and the attenuation
constant of 8 Neper/m or more can be achieved. In addition, when
the solid occupancy S is 8% or less, the weight can be reduced. The
solid occupancy S is preferably 1.35% or more and 7% or less, and
more preferably 1.4% or more and 6% or less.
[0032] The solid primarily includes fibers with an average fiber
diameter of 0.5 .mu.m or more and 20 .mu.m or less. The solid may
include fibers having a fiber diameter of 10 .mu.m or more and 30
.mu.m or less. It is sufficient that the average fiber diameter is
not less than 0.5 .mu.m and not more than 20 .mu.m. The solid may
also include low melting point fibers or tacky fibers for retaining
the shape of the porous fiber sheet 10. In addition, the solid may
contain antioxidants, porous stabilizers, viscosity modifiers,
colorants, and the like, to the extent that it does not impair
sound wave insulation.
[0033] The total thickness T0 of the porous fiber sheet 10 is, for
example, 1 mm or more and 100 mm or less. If the total thickness T0
is 1 mm or more, the shape of the porous fiber sheet 10 can be
maintained. In contrast, when the total thickness T0 is 100 mm or
less, the weight of the porous fiber sheet 10 can be reduced.
[0034] The porous fiber sheet 10 includes a plurality of nonwoven
fabric layers 20 that are separably and continuously arranged in a
predetermined in-plane direction (in the Z direction in FIG. 1)
between two opposing main surfaces 11, 12. Each of the plurality of
nonwoven layers 20 is made from a plurality of fibers that are
intertangled as seen from a predetermined in-plane direction (in
the Z direction in FIG. 1). Adjacent nonwoven layers 20 can be
easily peeled off at the interfaces from each other.
[0035] To enhance the peel strength of adjacent nonwoven layers 20,
crimped fibers connecting the nonwoven layers 20 may be inserted,
but such crimped fibers are not inserted in the present embodiment.
Because the fiber diameter is large and the specific surface area
is small, the energy attenuation by the viscous resistance of the
air is unlikely to be obtained, and the attenuation coefficient
becomes small.
[0036] A sound wave is a longitudinal wave (dense wave) that
propagates through vibrations of air density. As the density of air
changes in the gaps formed between fiber and fiber, a pressure
change caused by the change in the density of air occurs in the
fiber. If the same pressure change occurs simultaneously at any
part of a single fiber, the fiber resonates. The fiber resonates,
for example, when the fiber is positioned perpendicular to the
direction of propagation of the sound wave.
[0037] The larger the number of resonant fibers, the less likely
the sound wave is to be absorbed because the propagation of the
sound wave is easily blocked and the sound wave is more likely to
be reflected. The difficulty of sound wave transmission can be
evaluated with characteristic impedance. The higher the
characteristic impedance, the more likely the propagation of the
sound wave is hindered and the more likely the sound wave is
reflected, thereby reducing sound absorption properties.
[0038] Also, as the number of resonant fibers increases, the sound
wave propagation is more likely hindered and the attenuation of the
sound wave caused by the friction between the air and the fiber is
more likely prevented.
[0039] According to the present embodiment, as described above, a
plurality of nonwoven layers 20 is separably and continuously
arranged in the Z-direction. Therefore, when a sound wave is
incident in the X direction as shown by an arrow A in FIG. 1, the
number of fibers perpendicular to the direction of propagation of
the sound wave can be decreased in each nonwoven fabric layer 20,
and the resonance of the fibers can be inhibited in each nonwoven
fabric layer 20. As a result, the characteristic impedance of 1400
Ns/m.sup.3 or less can be achieved, and good sound absorption can
be achieved. In addition, the attenuation constant can be further
improved. A structure in which a plurality of nonwoven layers 20 is
continuously arranged in the Z-direction is referred to as a
longitudinal orientation.
[0040] If only the characteristic impedance (i.e., the impedance of
sound wave transmission) is reduced, it may be possible to reduce
the solid occupancy S to less than 1.3% (i.e., increase in the gap
ratio to 98.7% or more). In this case, because the attenuation
constant is too small and the sound insulation properties
deteriorate, the solid occupancy S is set to be 1.3% or more in the
present embodiment. By setting the solid occupancy S to 1.3% or
more and adopting a longitudinally oriented structure, sound
insulation and sound absorption can be achieved simultaneously.
This is particularly useful in applications that require the
function of both of the sound insulating material and the sound
absorbing material.
[0041] The nonwoven layer 20 is formed in a C-shape as seen in the
Y direction as shown in FIG. 1. The shape of the nonwoven layer 20
as seen in the Y direction is C-shaped in the present embodiment,
but is not particularly limited. For example, the nonwoven layer 20
may be formed in a wavelike fashion as shown in FIG. 2 or may be
linearly shaped as shown in FIG. 3. The shape of the nonwoven layer
20 as seen in the Y direction is a line diagonal to the Z direction
in FIG. 3, but may be a line perpendicular to the Z direction.
[0042] The porous fiber sheet 10 has a skin layer 21 on one of the
two opposing main surfaces 11, 12 and a skin layer 22 on the other
main surface 12. The two skin layers 21, 22, are each items of
intertangled fibers (i.e., nonwoven fabrics) as seen in the
thickness direction (the X direction in FIG. 1).
[0043] A plurality of nonwoven layers 20 is provided between the
two skin layers 21, 22, and each of the nonwoven layers 20 is
formed to be continuous with the two skin layers 21, 22. The
thickness of each of the skin layers 21, 22 is thin, and when
adjacent nonwoven layers 20 are peeled off at the interface from
each other, each of the skin layers 21, 22 become separated from
each other at the extended plane of the interface.
[0044] The thickness T1 of the skin layer 21 and the thickness T2
of the skin layer 22 are 0.01 mm or more and 5 mm or less. If the
thickness T1 and the thickness T2 are each 0.01 mm or more,
unintentional peeling at the interface of adjacent nonwoven layers
20 can be inhibited, and the shape is maintained. On the other
hand, if each of the thickness T1 and the thickness T2 is 5 mm or
less, the sound wave reflection by the skin layer 21 can be
reduced, and the attenuation of the sound wave in the nonwoven
layer 20 can be increased. The thicknesses T1 and T2 are each
preferably 0.3 mm or more and 4 mm or less, and more preferably 0.6
mm or more and 3 mm or less.
[0045] The porous fiber sheet 10 may be supported by a support
layer, such as an aluminum foil or a nonwoven fabric, for retaining
the shape. The support layer may be provided on both sides of the
porous fiber sheet 10 or on one side of the porous fiber sheet
10.
[0046] The method of manufacturing the porous fiber sheet 10 is not
particularly limited, but a melt spinning method is suitable, and a
melt blown method is particularly suitable. The melt blown process
involves blowing molten thermoplastic resin out of the nozzle and
stretching it into a fiber state at a high temperature and in a
high-speed airflow to spin the fibers on a collector. Thermoplastic
resins include at least one of a polyolefinic resin, a polyester
resin, and a polyamide resin.
[0047] The method of manufacturing the porous fiber sheet 10 is not
limited to the melt blown method, and may be, for example, an
electric field spinning method. According to the melt blown method
and the electric field spinning method, a nonwoven fabric is
obtained. The electric field spinning method allows for the
spinning of not only organic fibers but also inorganic fibers.
[0048] FIG. 4 is a perspective view illustrating a method of
manufacturing a porous fiber sheet according to a first embodiment.
The X direction, Y direction and Z direction in FIG. 4 are the same
as the X direction, Y direction and Z direction in FIG. 1. In FIG.
4, an arrow B is the direction of conveyance (Z direction) of the
porous fiber sheet 10. The manufacturing apparatus 50 for
manufacturing the porous fiber sheet 10 includes a die 51 and two
collectors 55, as shown in FIG. 4.
[0049] The die 51 includes a resin nozzle 52 for discharging molten
resin and gas nozzles 53 for discharging gas such as air. The resin
nozzle 52 discharges the molten resin vertically downward, for
example. The gas nozzles 53 are disposed on both sides of the resin
nozzle 52 in the X-direction, and each of the resin gas nozzles 53
discharges high temperature gas diagonally downward so as to
intersect the flow of molten resin discharged from the resin nozzle
52. The discharge port of the resin nozzle 52 and the discharge
ports of the gas nozzles 53 are disposed on the lower surface of
the die 51 spaced apart in the Y-direction. In the present
embodiment, the discharge direction of the resin nozzle 52 is in
the Z direction (in more detail, the vertical downward direction),
but the discharge direction may be inclined with respect to the Z
direction.
[0050] The opposing surfaces of the two collectors 55 are parallel,
and each of the two collectors 55 is perpendicular to the X
direction. A conveyance path of the porous fiber sheet 10 is formed
between the opposing surfaces of the two collectors 55. The porous
fiber sheet 10 is conveyed along with the endless belt 58 in the
Z-direction (more specifically vertically downward) and is bent and
horizontally conveyed after passing the space between the two
collectors 55. The total thickness T0 of the porous fiber sheet 10
(see FIG. 1) is smaller than the distance W between the two
collectors 55, for example, due to the self-weight and the like.
The distance W between the two collectors 55 is constant in the
present embodiment as shown in FIG. 4, but may be narrowed or
widened from the upstream side to the downstream side in the
conveying direction.
[0051] Each of the collectors 55 has, for example, a first pulley
56, a second pulley 57, and an endless belt 58 passing the path
between the first pulley 56 and the second pulley 57. The axial
direction of each of the rotational axes of the first pulley 56 and
the second pulley 57 is the Y direction. At least one of the first
pulley 56 and the second pulley 57 is a drive pulley that is
rotated by a drive unit such as a rotary motor. By continuously
rotating the drive pulley, the porous fiber sheet 10 is
continuously conveyed along the endless belt 58.
[0052] FIG. 5 is a diagram illustrating a fiber layer that passes
the path between the two collectors shown in FIG. 4. The molten
resin discharged from the resin nozzle 52 is stretched in the form
of fibers at a high-speed airflow discharged from the gas nozzle
53, thereby forming a fiber layer 29. The fiber layer 29 is a
nonwoven fabric in which a plurality of fibers are intertangled as
seen in the Z-direction view.
[0053] The fiber layer 29 bridges the path between the two
collectors 55 spaced in the X direction as seen in the Z-direction
view. The X-direction end of the fiber layer 29 is adhered near the
upper end of the endless belt 58 as shown in FIG. 4. The upper end
of the endless belt 58 is secured to the outer circumference of the
first pulley 56 and changes the orientation as the first pulley 56
rotates. This causes the X-direction end of the fiber layer 29 to
change its orientation, thereby forming the skin layers 21, 22.
Meanwhile, the central portion of the fiber layer 29 in the X
direction becomes the nonwoven fabric layer 20.
[0054] Note that each of the collectors 55 has an endless belt 58
in the present embodiment but does not need to have an endless belt
58. The at least one collector 55 may be comprised of a roll in
direct contact with the porous fiber sheet 10. In this case, the
roll may include a suction source for suctioning the porous fiber
sheet 10.
[0055] In the above-described first embodiment, a plurality of
nonwoven layers is arranged continuously in an in-plane direction,
but in the below-described second embodiment, a plurality of
nonwoven layers is continuously arranged in a thickness direction.
Hereinafter, major differences will be explained with reference to
FIGS. 6 and 7. A structure in which a plurality of nonwoven layers
is arranged continuously in an in-plane direction is referred to as
a longitudinal orientation, and a structure in which a plurality of
nonwoven layers is arranged continuously in a thickness direction
is similarly referred to as a transverse orientation.
[0056] FIG. 6 is a perspective view showing a porous fiber sheet
according to a second embodiment. In FIG. 6, the X direction, the Y
direction and the Z direction are perpendicular to each other. In
FIG. 6, unlike FIGS. 1 to 5 and the like, the Z direction is the
thickness direction of the porous fiber sheet. The X and Y
directions are the in-plane directions of the porous fiber
sheet.
[0057] In FIG. 6, an arrow A represents the incident direction of
the sound wave relative to the porous fiber sheet 10A. Note that in
FIG. 6, the sound wave is incident perpendicular to the main
surface 11A of the porous fiber sheet 10A, but may be incident
diagonally. Also, sound waves may be incident from both sides of
the porous fiber sheet 10A and may be incident on both sides of the
two main surfaces 11A, 12A.
[0058] The average fiber diameter of the porous fiber sheet 10A is
not less than 0.5 .mu.m and not more than 20 .mu.m, the same as the
average fiber diameter of the porous fiber sheet 10A according to
the first embodiment. Further, the solid occupancy S of the porous
fiber sheet 10A according to the present embodiment is not less
than 1.3% and not more than 8%, the same as the solid occupancy S
of the porous fiber sheet 10 according to the first embodiment.
Therefore, according to the present embodiment, similarly to the
above-described first embodiment, the sound wave is easily
attenuated by the friction between the fibers and the air having
the average fiber diameter of 0.5 .mu.m or more and 20 .mu.m or
less, and it is possible to achieve the attenuation constant of 8
Neper/m or more. Also, it is possible to reduce weight.
[0059] The porous fiber sheet 10A has a plurality of nonwoven
fabric layers 20A separably and continuously arranged in a
thickness direction (in FIG. 6, in the Z direction). Each of the
plurality of nonwoven layers 20A is one in which a plurality of
fibers are intertangled as seen in a thickness direction. Adjacent
nonwoven layers 20A can be easily peeled off at the interfaces from
each other.
[0060] FIG. 7 is a perspective view showing a method of
manufacturing a porous fiber sheet according to a second
embodiment. The X direction, Y direction, and Z direction in FIG. 7
are the same as the X direction, Y direction, and Z direction in
FIG. 6. In FIG. 7, an arrow B is the direction of conveyance (X
direction) of the porous fiber sheet.
[0061] A manufacturing apparatus 50A for manufacturing a porous
fiber sheet 10A includes a die 51A and a collector 55A, as shown in
FIG. 7. The die 51A has a resin nozzle 52A and gas nozzles 53A,
similarly to the die 51 of the first embodiment. In the present
embodiment, the discharge direction of the resin nozzle 52A is in
the Z direction (in more detail, in the vertical downward
direction), but the discharge direction may be inclined with
respect to the Z direction.
[0062] The collector 55A has an endless belt 58A passing between a
first pulley and a second pulley, which are not shown in the
drawing. The top surface of the endless belt 58A may be a
horizontal surface perpendicular to the Z direction. The porous
fiber sheet 10A is conveyed in the X direction with the endless
belt 58A while being gradually formed on the top surface of the
endless belt 58A.
EXAMPLE
[0063] Hereinafter, specific examples and comparative examples will
be described. Examples 1 to 8 described below include Examples 1 to
3 and Examples 5 to 7, and Examples 4 and 8 are comparative
examples.
Example 1
[0064] In Example 1, a transverse orientation of the porous fiber
sheet was produced by the melt blown method using the manufacturing
system 50A shown in FIG. 7. Moplen HP461Y, a polypropylene resin
manufactured by POLYMIRAE Company Ltd., was used as the raw
material for fibers. The polypropylene resin was melt-kneaded at
220 degrees C. in an extruder, and then delivered to the die 51A at
a discharge rate of 2.9 kg/h using a gear pump. The die 51A was
previously heated to 260 degrees C. The die 51A including 484 resin
nozzles 52A arranged in a row at a pitch of 0.72 mm in the Y
direction was used. The discharge direction of each resin nozzle
52A was in the Z direction (more specifically in the vertical
direction), and the diameter of the discharge port of each resin
nozzle 52A was 0.2 mm. A pair of gas nozzles 53A was provided on
both sides of each resin nozzle 52A in the X direction, and the air
flow rate from each gas nozzle 53A was 200 m/sec. The vertical
distance D (see FIG. 7) between the die 51A and the collector 55A
was made to be 500 mm. The top surface of the collector 55A was a
horizontal plane perpendicular to the Z direction. The transport
speed V of the porous fiber sheet by the collector 55A was 0.2
m/min. Using this, a transversely oriented product with an average
fiber diameter of 2.8 .mu.m, a total thickness of 52 mm, and a
solid occupancy of 1.6% was produced.
Example 2
[0065] In Example 2, a transversely oriented product was produced
under the same conditions as Example 1, except for the resin
discharge amount, the vertical distance D, and the conveyance speed
V. The resin discharge volume was 5.8 kg/h; the vertical distance D
was 700 mm; and the transfer speed V was 1.0 m/min. In the
conditions, a transversely oriented product was produced with an
average fiber diameter of 1.8 .mu.m, a total thickness of 13 mm,
and a solid occupancy of 2.5%.
Example 3
[0066] In Example 3, a transversely oriented product was produced
under the same conditions as Example 1, except for the conditions
of the air flow rate and the vertical distance D. The air flow rate
was 125 m/sec, and the vertical distance D was 700 mm. In the
conditions, a transversely oriented product was produced with an
average fiber diameter of 2.4 .mu.m, a total thickness of 28 mm,
and a solid occupancy of 3.2%.
Example 4
[0067] In Example 4, a transversely oriented product was produced
under the same conditions as Example 1, except for the vertical
distance D and the conveyance speed V. The vertical distance D was
700 mm, and the transfer speed V was 1.0 m/min. In the conditions,
a transversely oriented product was produced with an average fiber
diameter of 1.7 .mu.m, a total thickness of 16 mm, and a solid
occupancy of 0.8%.
Example 5
[0068] In Example 5, a porous fiber sheet was produced in a
longitudinal orientation by the melt blown method using the
manufacturing apparatus 50 shown in FIG. 4. Moplen HP461Y, a
polypropylene resin manufactured by POLYMIRAE Company Ltd., was
used as the raw material for fibers. The polypropylene resin was
melt-kneaded at 220 degrees C. in an extruder, and then delivered
to the die 51 at a discharge rate of 2.2 kg/h using a gear pump.
The die 51 was heated to 250 degrees C. in advance. The die 51 was
used including 484 resin nozzles 52 arranged in a row at a pitch of
0.72 mm in the Y direction. The discharge direction of each resin
nozzle 52 was in the Z direction (more specifically in the vertical
direction), and the diameter of the discharge port of each resin
nozzle 52 was 0.2 mm. A pair of gas nozzles 53 is provided on both
sides of each resin nozzle 52 in the X direction, and the air flow
rate from each gas nozzle 53 was set to 80 m/sec. In addition, the
vertical distance D (see FIG. 4) between the die 51 and each
collector 55 was made to be 400 mm. The distance between the two
collectors 55 was constant at 55 mm, and the conveyance speed V of
the porous fiber sheet by the two collectors 55 was set to 0.2
m/min. In the conditions, a longitudinally oriented product was
produced with an average fiber diameter of 3.5 .mu.m, a total
thickness of 44 mm, and a solid occupancy of 1.5%.
Example 6
[0069] In Example 6, a longitudinally oriented product was produced
under the same conditions as those in Example 5, except for the die
temperature, resin discharge volume, and transport speed V. The die
temperature was 260 degrees C.; the resin discharge rate was 2.9
kg/h; and the conveyance speed V was 0.3 m/min. In the conditions,
a longitudinal product was produced with an average fiber diameter
of 6.0 .mu.m, a total thickness of 33 mm, and a solid occupancy of
1.7%.
Example 7
[0070] In Example 7, a longitudinally oriented product was produced
under the same conditions as those in Example 5, except for the
resin discharge amount and the conveyance speed V. The resin
discharge rate was 2.9 kg/h, and the transfer speed V was 0.3
m/min. In the conditions, a longitudinally oriented product was
produced with an average fiber diameter of 7.6 .mu.m, a total
thickness of 45 mm, and a solid occupancy of 1.5%.
Example 8
[0071] In Example 8, a longitudinally oriented product was produced
under the same conditions as those in Example 5, except for the die
temperature, resin discharge amount, vertical distance D, and
conveyance speed V. The die temperature was 220 degrees C.; the
resin discharge volume was 2.9 kg/h; the vertical distance D was
300 mm; and the transfer speed V was 0.7 m/min. In the conditions,
a longitudinal orientation product was produced with an average
fiber diameter of 8.7 .mu.m, a total thickness of 32 mm, and a
solid occupancy of 0.6%.
[0072] [Summary of Manufacturing Conditions for Porous Fiber
Sheets]
[0073] Table 1 shows the manufacturing conditions for the porous
fiber sheet obtained in Examples 1 to 8.
TABLE-US-00001 TABLE 1 MANUFACTURING EXAMPLE EXAMPLE EXAMPLE
EXAMPLE EXAMPLE EXAMPLE EXAMPLE EXAMPLE CONDITIONS 1 2 3 4 5 6 7 8
TEMPERATURE OF 260 260 260 260 250 260 250 220 DIE (.degree. C.)
RESIN DISCHARGE 2.9 5.8 2.9 2.9 2.2 2.9 2.9 2.9 AMOUNT (kg/h)
DIAMETER OF 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 DISCHARGE PORT OF RESIN
NOZZLE (mm) AIR FLOW 200 200 125 200 80 80 80 80 SPEED (m/sec)
DISTANCE BETWEEN 500 700 700 700 400 400 400 300 DIE AND COLLECTOR
(mm) DISTANCE BETWEEN TWO -- -- -- -- 55 55 55 55 COLLECTORS (mm)
CONVEYANCE SPEED OF 0.2 1.0 0.2 1.0 0.2 0.3 0.3 0.7 COLLECTOR
(m/min)
[0074] A representative example of a transversely oriented product
obtained in Examples 1 to 4 is shown in FIG. 8, which is a
transversely oriented product obtained in Example 1. The X
direction, the Y direction, and the Z direction of FIG. 8 are the
same as the X direction, the Y direction, and the Z direction of
FIG. 7. As a representative example of the transversely oriented
product obtained in Examples 5 to 8, the longitudinally oriented
product obtained in Example 5 is shown in FIG. 9. The X direction,
the Y direction, and the Z direction of FIG. 9 are the same as the
X direction, the Y direction, and the Z direction of FIG. 4.
[0075] [Evaluation Method for Porous Fiber Sheet]
[0076] The following measurements were performed on the porous
fiber sheet obtained in Examples 1 to 8. The thickness of the skin
layer was measured only for the longitudinal orientation of the
porous fiber sheet obtained in Examples 5 to 8.
[0077] <Total Thickness of Porous Fiber Sheet>
[0078] The total thickness of the porous fiber sheet was determined
by placing the test piece cut from the porous fiber sheet on the
horizontal mounting surface of the table, and measuring the
thickness of five points near the center of the test piece with a
thickness gauge as seen from above, thereby obtaining the
arithmetic mean value of the measured values of the five points.
The test pieces were cut into rectangular shapes of 100 mm long and
100 mm wide as seen from a direction perpendicular to the main
surface of the porous fiber sheet. The test pieces were placed on a
placement surface of the platform so that the cut surface of the
test piece was perpendicular to the placement surface of the
platform.
[0079] <Skin Layer Thickness>
[0080] The thickness of the skin layer was measured by a thickness
gauge at three points in each of the two skin layers of the test
piece cut from the porous fiber sheet to obtain the arithmetic mean
of the six measurement values. The test piece was cut into a
rectangular shape of 100 mm in length and 100 mm in width, from the
center in the Y direction of the porous fiber sheet (see FIGS. 1
and 2), as seen in the direction perpendicular to the main surface
of the porous fiber sheet. Note that, the arithmetic mean value of
the thickness of the three points of one skin layer and the
arithmetic mean value of the thickness of the three points of the
other skin layer were the same within the range of error.
[0081] <Average Fiber Diameter of Porous Fiber Sheet>
[0082] The average fiber diameter of the porous fiber sheet was
measured by image analysis of SEM photographs (scanning electron
micrographs) of test pieces cut from the porous fiber sheet. The
test pieces were cut into a rectangular shape of 5 mm long and 10
mm wide as seen from a direction perpendicular to the main surface
of the porous fiber sheet. A Pt film was deposited in advance using
a sputtering device on the cross section for measuring the average
fiber diameter of the test pieces.
[0083] The magnetron sputtering device MSP-15 manufactured by
Vacuum Device Co. Ltd. was used as the sputtering device. The
current value was 30 mA and the deposition time was 30 seconds.
[0084] As a scanning electron microscope (SEM), the proX PREMIUMI
II manufactured by Phenom-World was used. The beam energy of the
electron beam was 10 KeV. Electronic images were acquired using the
Automated Image Mapping system of the Phenom-World Pro Suite phenom
application system at a magnification of 1,500-fold while changing
the imaging location.
[0085] A total of 1,000 fiber diameters were measured from 30
electronic images using image analysis, and the measured arithmetic
mean fiber diameters were used as the mean fiber diameters. Image
analysis was performed using the fiber metric function of the Pro
Suite Phenom Application system from Phenom-World.
[0086] <Percentage of Solids in Porous Fiber Sheets>
[0087] The solid occupancy of the porous fiber sheet was calculated
as the value obtained by dividing the bulk density (BD) of the
porous fiber sheet by the true density (TD) of the solid (BD/TD)
and multiplying by 100 (BD/TD.times.100).
[0088] The bulk density (BD) of the porous fiber sheet was obtained
by dividing the mass of the test piece cut from the porous fiber
sheet by the volume of the test piece. The specimens were cut into
100.5 mm diameter circles in a direction perpendicular to the main
surface of the porous fiber sheet. The test piece volume was
measured by multiplying the circular area of 100.5 mm diameter by
the total thickness of the porous fiber sheet. The mass of the test
piece was measured by an electronic scale.
[0089] The true density of the fibers that constitute the solid was
used as the true density of the solid. The true density of the
polypropylene resin Moplen HP461Y, manufactured by POLYMIRAE Co.
Ltd., used as the fiber material, was 920 kg/m.sup.3.
[0090] <Attenuation Constant of Porous Fiber Sheet>
[0091] The attenuation constant (in Neper/m) of the porous fiber
sheet was measured in accordance with JIS A 1405-2 using a vertical
incidence sound absorption measurement system WinZacMTX
manufactured by Japan Acoustic Engineering Co. Ltd. Specifically, a
sound wave was perpendicularly emitted to a flat plane on one side
of the cylindrical test piece used to measure the solid occupancy,
and the attenuation constant of the sound wave was measured when
the frequency of the sound wave was varied from 200 Hz to 1000 Hz
at 20 Hz pitch, and the arithmetic mean of the measured values at
41 points was used as the attenuation constant of the porous fiber
sheet.
[0092] Attenuation constants with frequencies less than 200 Hz were
excluded from the measurement because of the large measurement
error.
<Characteristic Impedance of Porous Fiber Sheet>
[0093] The characteristic impedance (in Ns/m.sup.3) of the porous
fiber sheet was measured in accordance with JIS A 1405-2 using the
vertical incidence sound absorption coefficient measurement system
WinZacMTX manufactured by Nihon Onkyo Engineering Co., Ltd. in the
same manner as the attenuation constant. Specifically, each
characteristic impedance (more specifically, the real part of the
characteristic impedance) was measured when the sound wave
frequency was varied from 200 Hz to 1000 Hz at a 20 Hz pitch by
causing the sound wave to be incident perpendicularly to the flat
plane on one side of the cylindrical test piece used to measure the
solid occupancy, and the arithmetic mean of the values of 41 points
was used as the characteristic impedance of the porous fiber
sheet.
[0094] [Evaluation Results for Porous Fiber Sheet]
[0095] Table 2 shows the evaluation results of the porous fiber
sheet obtained in Examples 1 to 8.
TABLE-US-00002 TABLE 2 EXAMPLE EXAMPLE EXAMPLE EXAMPLE EXAMPLE
EXAMPLE EXAMPLE EXAMPLE EVALUATION ITEM 1 2 3 4 5 6 7 8 TOTAL
THICKNESS 52 13 28 16 44 33 45 32 (mm) SKIN LAYER -- -- -- -- 0.74
0.72 0.80 0.61 THICKNESS (mm) SOLID 1.6 2.5 3.2 0.8 1.5 1.7 1.5 0.6
OCCUPANCY (%) AVERAGE FIBER 2.8 1.8 2.4 1.7 3.5 6.0 7.6 8.7
DIAMETER (.mu.m) ATTENUATION 8.0 13.7 15.7 5.4 10.5 10.1 9.2 2.7
CONSTANT (Neper/m) CHARACTERISTIC 1185 1597 1614 685 876 793 761
691 IMPEDANCE (N s/m.sup.3)
[0096] The porous fiber sheets obtained in Examples 1 to 3 and
Examples 5 to 7 had an average fiber diameter in the range from 0.5
.mu.m to 20 .mu.m and a solid occupancy S in the range from 1.3% to
8% or less, thereby obtaining a high attenuation constant (8
Neper/m or more). In contrast, the porous fiber sheet obtained in
Examples 4 and 8 had a low attenuation constant because of its
solid occupancy less than 1.3%.
[0097] Among Examples 1 to 3 and Examples 5 to 7, the porous fiber
sheet of Examples 5 to 7 was a longitudinally oriented product,
thereby obtaining a low characteristic impedance (1400 Ns/m.sup.3
or less). In contrast, the porous fiber sheets of Examples 1 to 3
were transversely oriented, and thus exhibited a high
characteristic impedance. Furthermore, as is evident from the
comparison between Example 1 and Example 5, when the mean fiber
diameter and the solids occupancy are approximately the same, the
attenuation constant can be improved more in the longitudinally
oriented product than in the horizontally oriented product.
[0098] Although the embodiments of the porous fiber sheet and the
like have been described, the present invention is not limited to
the above-described embodiments and the like, and various
alternations and modifications can be made within the scope of the
subject matter of the present invention as claimed.
[0099] For example, the porous fiber sheets of the above
embodiments are used as sound insulating materials to attenuate
incoming sound waves, but may be used for applications other than
sound insulating materials. Applications other than sound
insulating materials include thermal insulating materials,
vibration damping materials, or shock absorbing materials.
[0100] This application is based upon and claims priority to
Japanese Patent Application No. 2017-227447 filed with the Japanese
Patent Office on Nov. 28, 2017, the entire contents of which are
hereby incorporated by reference.
DESCRIPTION OF THE REFERENCE NUMERALS
[0101] 10 porous fiber sheet
[0102] 11,12 main surface
[0103] 20 nonwoven layer
[0104] 21,22 skin layer
* * * * *